Fungicide offers hope for root rot control

John Wilde looked over a field of cotton near his San Angelo, Texas farm and noted the differences between several test plots on one side of a field road. Some plots looked healthy with potential to make exceptional yields; others showed large areas of dead cotton stalks and poor yield prospects.

He looked to the other side of that narrow path, where no trials have been applied, and figured yield loss will be 50 percent or higher.

Wilde and his son Doug have turned this cotton patch over to Texas AgriLife Research and Extension scientists who are using it to test control options for cotton root rot, a devastating disease that costs Southern Rolling Plains farmers thousands of dollars every year.

“This is a root rot nursery,” Wilde says. “Usually, we would rotate this field out of cotton to corn to manage root rot, but we know that it’s a good place to test control options.” He says the sacrifice will be worth the trouble if scientists find a viable control for root rot.

They may be close. After testing several fungicides through subsurface drip irrigation injection for several years, Extension IPM specialist Rick Minzenmayer and Extension plant pathologist Tom Isakeit discovered that flutriafol, a fungicide labeled only for soybeans and apples, will control the fungus that causes root rot. (Early results were reported in a Southwest Farm Press article last December.)

Yield advantage

David Drake, an Extension agronomist who came on board at the San Angelo Research and Extension Center last year, says yield results from 2009 tests indicate as much as a 500-pound per acre yield advantage in flutriafol treated plots.Although the best results came from high rates, lower rates similar to labeled rates on other crops also reduced disease and gave a yield increase.

In 2010 trials, the research emphasis was on evaluating lower rates with different application methods and in different production areas of Texas. Results from these trials in the San Angelo area and other areas of Texas were mostly encouraging. The data will be used to support a label for this fungicide on cotton further down the road.

A key sticking point to getting an EPA label may be residual activity. The product appears to persist in the soil from one year to the next. Plots treated one year in Wilde’s field and untreated the next continue to show good control. However, persistence of a chemical in soil is not a good characteristic in the eyes of the EPA.

Drake says that flutriafol is a “pretty stable product,” and stays where it’s applied. Leaching potential is uncertain. “It does not appear that the product moves, but we’re still looking. We need to determine the best rate, have the residue work done, and then get a label.”

This year has been a bad one for root rot throughout the Rolling Plains. “Throughout the Rolling Plains and into the Blacklands, we’ve seen perhaps a 20 percent crop loss from root rot,” Drake says. “Heavy July rainfall seemed to encourage it.”

New options needed

In the past, farmers with root rot infections had only one option—rotation. Drake says wheat and grain sorghum are possibilities. “But we’ve seen fields following two years of wheat with terrible root rot.”

No varietal resistance exists. “Rotation or some kind of chemical are our only options,” Drake says. “Old literature suggested adding manure or other organic matter and deep plowing, but those options are not viable for most growers. Root rot remains a devastating disease.”

“Root rot is a significant economic factor throughout the Southern Rolling Plains,” Minzenmayer says. “I fully realize the effect it has on farmers after harvesting plots this fall. Dead stalks break off and go into the stripper where they either get crushed and pushed into the basket and cause quality problems or they clog up the machinery.”

He says farmers with heavy root rot infestations often have to climb off strippers every few feet to unclog the machinery. “I’ve seen fields with 3-bale yield potential that have stretches of 30 to 40 feet with nothing on the stalks.”

They initially concentrated on injecting the material through drip irrigation tape on the Wilde farm. That research showed that applying the material directly under the row instead of in the middles (where some irrigation tape is located) works best since the material does not appear to move.

They’ve also looked at adding the product to liquid fertilizer and applying with a fertilization rig. “It did not combine well with the liquid fertilizer,” Drake says.

They tried treating seed but found they could not get enough concentration on the seed to be effective. Applying the product on corncob granules at planting seemed to work, “but the company does not want to develop a granular formulation at this time,” Drake says.

They tried to knife in the material during the growing season and got no response.

Liquid formulation

This year they tested a liquid formulation applied at planting in the furrow with a seed firmer (used similar to a pop-up fertilizer application). “We can mix flutriafol with water and put it right into the seed bed, before the seed is covered,” Minzenmayer says. “That technique looks good even at lower rates.”

They say the at-planting, liquid treatment offers farmers who use drip, pivot or flood irrigation, as well as dryland producers, an opportunity to apply the material.

They’ve tested a stem drench, spraying the material at the base of the plant in-season. “We’ve run trials with pivot irrigation and flood irrigation,” Drake says. “We got a response with the pivot, but not flood irrigation.” Isakeit observed disease reduction with stem drenches in dryland cotton in Blacklands and Upper Coast trials. An early timing, weeks before the appearance of disease, was critical for effectiveness. However, this approach is probably not feasible for most growers.

Variable Rate Application technology may play a role, as well. Using infrared imagery or other technology to identify and map root rot hot spots, farmers may be able to apply material just where it’s needed, not to an entire field.

The one drawback to that possibility may be the inconsistency of the disease. “Infection is sometimes hit-or-miss,” Drake says. “We can’t always be sure it will show up in the same place the next year. It’s a fungal disease so it needs to have a susceptible plant and the proper environmental conditions to develop.”

He says it often starts in a circle and moves outward, but plants within the circle are often missed.

Minzenmayer says finding an effective product represents a significant achievement in managing root rot. But they need to refine rates and application techniques before it’s ready for widespread use. “In 2011 we will fine-tune rates and find an effective range.”

Drake says farmers will come up with new ideas on how to apply the material once it’s approved. In the meantime, he recommends patience.